Semiconductor device

ABSTRACT

The semiconductor device of the present embodiment includes a lead frame having a projection portion, the projection portion having an upper face and a side face, a semiconductor chip provided above the projection portion, and a bonding material provided between the projection portion and the semiconductor chip, the bonding material being in contact with the upper face and the side face, the bonding material bonding the lead frame and the semiconductor chip.

CROSS-REFERENCE TO RELATED APPLICATION

This application is based upon and claims the benefit of priority fromJapanese Patent Application No. 2019-163440, filed on Sep. 6, 2019, theentire contents of which are incorporated herein by reference.

FIELD

Embodiments described herein relate generally to a semiconductor device.

BACKGROUND

Power semiconductor chips designed for power control have been developedwhich are a metal-oxide-semiconductor field-effect-transistor (MOSFET),an insulated gate bipolar transistor (IGBT) and the like used in a widerange of fields such as power generation and power transmission,rotating machines such as pumps and blowers, power supplies forcommunication systems and factories, railways with AC motors, electricvehicles, and home electric appliances.

Further, development of a semiconductor device as a power moduleincluding such a power semiconductor chip has been performed. Suchsemiconductor devices are required to have specifications such as highcurrent density, low loss, and high heat dissipation.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1A and 1B are schematic cross-sectional views of a semiconductordevice of a first embodiment;

FIGS. 2A and 2B are schematic views showing the shape of the chip faceand the shape of the upper face of the projection portion of the firstembodiment;

FIGS. 3A to 3D are schematic cross-sectional views showing thesemiconductor device in the process of manufacture in the manufacturingmethod of the semiconductor device of the first embodiment;

FIG. 4 is a flowchart of a manufacturing method of the semiconductordevice of the first embodiment;

FIGS. 5A and 5B are schematic cross-sectional views of a semiconductordevice that is a comparative example of the first embodiment; and

FIG. 6 is a schematic cross-sectional view of a semiconductor device ofa second embodiment.

DETAILED DESCRIPTION

Hereinafter, embodiments of the present disclosure will be describedwith reference to the drawings. In the following description, the sameor similar members may be denoted by the same reference numerals.Further, description of members once described may be omitted asappropriate.

In the present specification, the upper direction of the drawing isdescribed as “upper” and the lower direction of the drawing as “lower”in order to indicate the positional relationship of parts and the like.In the present specification, the terms “upper” and “lower” are notnecessarily terms indicating the relationship with the direction ofgravity.

First Embodiment

The semiconductor device of the present embodiment includes a lead framehaving a projection portion, the projection portion having an upper faceand a side face, a semiconductor chip provided above the projectionportion, and a bonding material provided between the projection portionand the semiconductor chip, the bonding material being in contact withthe upper face and the side face, the bonding material bonding the leadframe and the semiconductor chip.

FIGS. 1A and 1B are schematic cross-sectional views of a semiconductordevice 100 of an embodiment;

FIG. 1A is a schematic cross-sectional view of a semiconductor device100 of according to an aspect of the present embodiment.

The semiconductor device 100 includes a lead frame 10, a semiconductorchip 20, and a bonding material 30.

The lead frame 10 is formed of a metal such as copper (Cu) or an alloy,for example. The surface of the lead frame 10 may be provided with athin film (not shown) including, for example, gold (Au), platinum (Pt),palladium (Pd), silver (Ag), copper (Cu), tin (Sri), nickel (Ni), or thelike.

The lead frame 10 has a projection portion 12. In FIG. 1A, the upperface 14 and the side face 16 of the projection portion 12 and the upperface 11 of the lead frame around the projection portion 12 are alsoshown.

The height h₁ of the projection portion 12 is preferably 20 μm or moreand 35 μm, or less.

The semiconductor chip 20 is provided above the projection portion 12.The semiconductor chip 20 has a side face 22, an upper face 24, and achip face (lower face) 26.

The semiconductor chip 20 is, for example, a vertical Si-IGBT includingsilicon (Si). The semiconductor chip 20 may be an Si-MOSFET, a fastrecovery diode (Si-FRD), an SiC-IGBT including silicon carbide (SiC), anSiC-MOSFET or a schottky barrier diode (SiC-SBD), or a GaN-MOSFETincluding a nitride semiconductor in which the group V element isnitrogen in a III-V group semiconductor. The semiconductor chip 20 maynot be a so-called power semiconductor chip.

The chip thickness of the semiconductor chip 20 is, for example, about250 μm. Note that the chip thickness of the semiconductor chip 20 is notlimited to this.

The bonding material 30 is provided between the projection portion 12and the semiconductor chip 20. The bonding material 30 is in contactwith the upper face 14 and the side face 16 of the projection portion 12to bond the lead frame 10 and the semiconductor chip 20.

Although the bonding material 30 is not particularly limited, forexample, a die attach material including an insulator such as an epoxydie attach material, a silicone die attach material, a polyimide dieattach material, an acrylic die attach material, or the like, or a dieattach material including a material having electrical conductivity ispreferably used. For example, when the bonding material 30 is a dieattach material including a material having electrical conductivity, andthe semiconductor chip 20 is a vertical Si-IGBT including silicon (Si),the current flowing through the semiconductor chip 20 flows into thelead frame 10 including the projection portion 12 of the bondingmaterial 30 via the bonding material 30.

FIG. 1B is a schematic cross-sectional view of a semiconductor deviceaccording to another aspect of the present embodiment. The bondingmaterial 30 spreads over and contacts the upper face 11 of the leadframe around the projection portion 12.

FIGS. 2A and 2B are schematic views showing the shape of a chip face 26and the shape of the upper face 14 of the projection portion 12 of theembodiment.

In FIG. 2A, the shape of the chip face 26 and the shape of the upperface 14 of the projection portion 12 are both square. In FIG. 2B, theshape of the chip face 26 and the shape of the upper face 14 of theprojection portion 12 are both rectangular. Note that the shape of thechip face 26 and the shape of the upper face 14 of the projectionportion 12 are not limited to this, and may be, for example, a triangleor a circle.

When the area of the chip face 26 of the semiconductor chip 20 is S₁,and the area of the upper face 14 of the projection portion 12 is S₂, itis preferable that 0.7S₁≤S₂≤0.9S₁ be satisfied.

The shape of the chip face 26 and the shape of the upper face 14 of theprojection portion 12 are preferably similar to each other. In FIG. 2A,the shape of the chip face 26 and the shape of the upper face 14 of theprojection portion 12 are both square and similar to each other. In FIG.2B, the shape of the chip face 26 and the shape of the upper face 14 ofthe projection portion 12 are both rectangular and similar to eachother.

FIGS. 3A to 3D are schematic cross-sectional views showing thesemiconductor device 100 in the process of manufacture in themanufacturing method of the semiconductor device 100 of the embodiment.FIG. 4 is a flowchart of the manufacturing method of the semiconductordevice 100 of the present embodiment.

First, the lead frame 10 having the projection portion 12 is prepared.Here, the projection portion 12 is formed, for example, by etching orcoining of the lead frame 10 (FIG. 3A, FIG. 4 (S10)).

Next, an unsolidified bonding material 32 is applied on the upper face14 of the projection portion 12 (FIG. 3B, FIG. 4 (S20)).

Next, the semiconductor chip 20 is placed on the unsolidified bondingmaterial 32. At this time, the unsolidified bonding material 32protrudes from the side face 16 of the projection portion and contactsthe side face 16 of the projection portion. Although not shown, theunsolidified bonding material 32 may protrude from the upper face 11 ofthe lead frame 10 around the projection portion 12 and may be in contactwith the upper face 11 of the lead frame 10 around the projectionportion 12 (FIG. 3C, FIG. 4 (S30)). Further, the unsolidified bondingmaterial 32 may spread over and contact the upper face 11 of the leadframe around the projection portion 12.

Next, in a state where the semiconductor chip 20 is placed, the leadframe 10, the unsolidified bonding material 32, and the semiconductorchip 20 are heat-treated. Thereby, the unsolidified bonding material 30is solidified to become the bonding material 30, and bonds the leadframe 10 and the semiconductor chip 20 to obtain the semiconductordevice 100 of this embodiment (FIG. 3D, FIG. 4 (S40)).

Next, the function and effect of the semiconductor device 100 of thepresent embodiment will be described.

FIGS. 5A and 5B are schematic cross-sectional views of a semiconductordevice that is a comparative example of the present embodiment. FIG. 5Ais a schematic cross-sectional view of a semiconductor device 800 thatis a comparative embodiment of the present embodiment, and FIG. 5B is aschematic cross-sectional view of a semiconductor device 810 that is acomparative embodiment of the present embodiment.

When the semiconductor chip 20 is placed on the lead frame, the bondingmaterial 30 is used. Here, when the semiconductor chip 20 is placed onthe unsolidified bonding material 32, part of the unsolidified bondingmaterial 32 spreads from the lower side of the semiconductor chip 20.There is a problem that the bonding material 30 contacts the side face22 of the semiconductor chip 20 (FIG. 5A), or the bonding material 30contacts the upper face 24 of the semiconductor chip (FIG. 5B). Inparticular, when the bonding material 30 has conductivity, there is aproblem that the electrode provided on the upper face 24 of thesemiconductor chip 20 and the electrode provided on the chip face (lowerface) 26 of the semiconductor chip are short-circuited.

In order to solve this problem, it is conceivable to increase the filmthickness of the semiconductor chip 20. However, particularly in thecase of a vertical Si-IGBT or the like, there is a problem that theon-resistance increases as the film thickness of the semiconductor chip20 increases.

When the film thickness of the semiconductor chip 20 is thin, by using asheet-like die attach film (DAF) as the bonding material 30, the problemthat the bonding material 30 contacts the side face 22 and the upperface 24 of the semiconductor chip 20 can be avoided. However, since thedie attach film is expensive, there is a problem that it is difficult toapply the die attach film to the semiconductor chip 20 having a low unitprice.

In the semiconductor device of this embodiment, the lead frame 10 hasthe projection portion 12. The semiconductor chip 20 is provided abovethe projection portion 12, and is bonded using a bonding material 30provided between the semiconductor chip 20 and the projection portion12.

By providing the projection portion 12, when the semiconductor chap 20is placed on the unsolidified bonding material 32, the unsolidifiedbonding material 32 spreads over the side face 16 of the projectionportion 12, and spreads over and contacts the side face 16 of theprojection portion 12 or the upper face 11 of the lead frame around theprojection portion 12. As a result, it is possible to suppress thecontact of the bonding material 30 with the side face 22 and the upperface 24 of the semiconductor chip 20, thus a semiconductor device withimproved reliability can be provided.

When the area of the chip face 26 of the semiconductor chip 20 is S₁,and the area of the upper face 14 of the projection portion 12 is S₂, itis preferable that 0.7S₁≤S₂≤0.9S₁ satisfied. When S₂<0.7S₁ is satisfied,since the area S₂ of the upper face 14 of the projection portion 12 istoo small, the semiconductor chip 20 may not be fixed onto theprojection portion 12. In addition, since the projection portion 12 istoo small, there is a possibility that the resistance between thesemiconductor chip 20 and the lead frame 10 may increase when thecurrent flowing through the semiconductor chip 20 flows into theprojection portion 12. On the other hand, when 0.9S₁<S₂ is satisfied,since the area S₂ of the upper face 14 of the projection portion 12 istoo large, there is a possibility that the entire unsolidified bondingmaterial 32 is not placed within the side face 16 of the projectionportion 12 or the upper face 11 of the lead frame, and contacts the sideface 22 and the upper face 24 of the semiconductor chip 20.

The shape of the chip face 26 of the semiconductor chip 20 and the shapeof the upper face 14 of the projection portion 12 are preferably similarto each other. This is because the bonding material 30 is distributed asuniformly as possible on the side face 16 of the projection portion 12and the upper face 11 of the lead frame around the projection portion 12to further improve the reliability.

The height h₁ of the projection portion 12 is preferably 20 μm or moreand 35 μm or less. When the height h₁ of the projection portion 12 isless than 20 μm, since the height h₁ of the projection portion 12 is toolow, there is a possibility that the entire unsolidified bondingmaterial 32 is not placed within the side face 16 of the projectionportion 12 or the upper face 11 of the lead frame, and contacts the sideface or the upper face of the semiconductor chip 20. On the other hand,when the height h₁ of the projection portion 12 exceeds 35 μm, since theprojection portion 12 is too high, the resistance between thesemiconductor chip 20 and the lead frame 10 may increase.

According to the semiconductor device of the present embodiment, it ispossible to provide the semiconductor device with improved reliability.

Second Embodiment

The semiconductor device of the present embodiment is different from thesemiconductor device of the first embodiment in that the angle formed bythe side face 16 of the projection portion 12 and the upper face 11 ofthe lead frame 10 around the projection portion 12 is greater than 90degrees. Here, the description of the second embodiment overlapping thatof the first embodiment will be omitted.

FIG. 6 is a schematic cross-sectional view of a semiconductor device 200according to the present embodiment.

In the semiconductor device 200, the angle θ formed by the side face 16of the projection portion 12 and the upper face 11 of the lead frame 10around the projection portion 12 is larger than 90 degrees.

The unsolidified bonding material 32 may contain bubbles. The bubblesare likely to stay in the portion 18 where the side face 16 of theprojection portion 12 and the upper face 11 of the lead frame around theprojection portion intersect and in its vicinity. When the unsolidifiedbonding material 32 is solidified to contain the bubbles and becomes thebonding material 30, the bubbles repeatedly contract with the thermalcycle of the semiconductor device, thus deterioration of the bondingmaterial 30 such as cracks may occur. When the angle θ is larger than 90degrees, the bubbles easily pass through upward the side face 16 of theprojection portion 12 and escape. Therefore, this problem can beavoided.

According to the semiconductor device of the present embodiment, it ispossible to provide the semiconductor device with improved reliability.

While certain embodiments have been described, these embodiments havebees presented by way of example only, and are not intended to limit thescope of the inventions. Indeed, the semiconductor device describedherein may be embodied in a variety of other forms; also, variousomissions, substitutions and changes in the form of the devices andmethods described herein may be made without departing from the spiritof the inventions. The accompanying claims and their equivalents areintended to cover such forms or modifications as would fall within thescope and spirit of the inventions.

What is claimed is:
 1. A semiconductor device comprising: a lead framehaving a projection portion and a first upper face provided around theprojection portion, the projection portion having a second upper faceand a plurality of side faces, a shape of the second upper face being arectangle, and the first upper face being directly connected with eachof the side faces; a semiconductor chip having a chip face, thesemiconductor chip being provided above the projection portion, a widthof the second upper face of the projection portion being shorter than awidth of the chip face of the semiconductor chip, an area of the secondupper face of the projection portion being smaller than an area of thechip face of the semiconductor chip; and a bonding material providedbetween the projection portion and the semiconductor chip, the bondingmaterial being in direct contact with the semiconductor chip, the secondupper face of the projection portion and the side faces of theprojection portion, and the bonding material bonding the lead frame andthe semiconductor chip.
 2. The semiconductor device according to claim1, wherein 0.7S₁≤S₂≤0.9S₁ is satisfied, where S₁ is an area of the chipface of the semiconductor chip and S₂ is an area of the second upperface of the projection portion.
 3. The semiconductor device according toclaim 2, wherein a shape of the chip face and a shape of the secondupper face are similar to each other.
 4. The semiconductor deviceaccording to claim 1, wherein the projection portion has a height of 20μm or more and 35 μm or less.
 5. The semiconductor device according toclaim 1, wherein an angle formed by the side face of the projectionportion and the first upper face of the lead frame around the projectionportion is greater than 90 degrees.
 6. The semiconductor deviceaccording to claim 1, wherein the bonding material is in contact withthe first upper face of the lead frame around the projection portion. 7.The semiconductor device according to claim 1, wherein the bondingmaterial has electrical conductivity.
 8. The semiconductor deviceaccording to claim 1, wherein a wire is not connected to thesemiconductor chip.
 9. The semiconductor device according to claim 1,wherein an angle formed by the side face of the projection portion andthe first upper face of the lead frame around the projection portion is90 degrees.
 10. The semiconductor device according to claim 1, whereinthe bonding material is provided apart from the first upper face of thelead frame around the projection portion.